It was an adventure that was years in the making, one that would lead two Polson High School graduates and their friends on an 8,000-mile sailing voyage from Hawaii to New Zealand over seven months.

The Voyage of the Shannon actually started back in 2006, when Kevin O’Brien and fellow Polson graduate Christine Hoe and a college buddy from Hawaii, Ken Bwy, bought a 36-foot Union sailboat in San Francisco. They sailed the Shannon to Hawaii and spent the next few years working and preparing for an epic South Pacific cruise.

“We worked and saved and fixed the boat up for a couple of years. We just slowly added improvements,” said O’Brien, who went on to graduate from the University of Hawaii before becoming a marine biologist with the National Oceanic and Atmospheric Administration.

The Shannon set sail from Hawaii last May 6 with two extra hands on board — Bwy’s wife, Alina Madadi-Bwy, and Britton Warfield, a former Marine who had previously served in Afghanistan.

The first leg was the longest, a southerly sail into the wind to reach the Marquesas Islands.

“We sailed 32 days into the wind basically the whole way,” O’Brien said. “We had been wanting to see the Marquesas the whole time we were getting ready. That was probably the hardest leg.”

At one point near the Equator, the crew encountered the doldrums — a complete absence of wind — and were left to drift on currents for about four days.

“We were sort of expecting it, but it was a little worse than we thought. We had a small fuel tank and very limited motoring range,” said O’Brien, adding that the Shannon eventually drifted into some wind and got back under way.

They reached a deep-water area with cold upwellings that brought up an abundance of sea life.

“We had one night where the flying fish bombarded the boat, and came flying in through the open hatches,” O’Brien said.

The Voyage of the Shannon evolved into an adventure rich in cultural as well as natural experiences.

“The Marquesas were beautiful,” O’Brien said. “The people were the most friendly that we met. We didn’t encounter any other people quite like them on the rest of the trip.”

Although no one on the crew spoke French, they managed to get along well with their hosts, visiting about seven islands. After five weeks, they sailed on to Tuamotus, a chain of shallow water atolls.

“There’s no significant land mass. But the coral reefs and the sea life were amazing,” O’Brien said. “We spent a lot of our time free-diving and spear-fishing and what not.”

While they saw plenty of reef sharks, O’Brien at one point speared a large fish, luring in an oceanic white tip shark.

They sailed on to Tahiti, where they spent considerable time on needed boat repairs, and then on to the Cook Islands, where they encountered people who spoke English for the first time on the trip.

Along the duration of the voyage, O’Brien and the two women were regularly posting narratives of their experiences online for a Reach the World education program designed for inner-city schools.

“We had schools in New York City, Chicago and Hawaii following,” O’Brien said. “I gave the link to some teachers in Polson, so I know some of them were watching too.”

One of the most interesting stops was a place called Palmerston Atoll, which is inhabited by a single extended family with ancestors who settled there in the 1860s, somehow carrying on with very strict rules that prohibit inbreeding.

“They all have the same last name — Marsters,” O’Brien said. “It was sort of a neat out-of-the-century experience.”

At the Tongan island of Tofua, the crew swam with humpback whales and hiked up to an active volcano crater. They sailed on, reaching New Zealand on Nov. 9.

“We had to get to New Zealand by November to get out of the tropics before the hurricane season,” which runs from November through April.

O’Brien and Hoe remained in New Zealand for about a month before returning to Montana for Christmas. Since then, O’Brien said he’s been staying with his parents and doing a lot of cross-country skiing. He returns to his NOAA job in Hawaii Jan. 18.

The Shannon remains dry docked in New Zealand.

“We’ll probably get back down there in 2012,” O’Brien said. “There’s a possibility we could sell it too. But for now, it’s just sitting in the boat yard.”

The overall adventure was unforgettable.

“It was great,” O’Brien said. “They were just some really interesting places and nature-wise it was pretty incredible too.”